User Defined Functions

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1 User Defined Functions Aaron S. Donahue Department of Civil and Environmental Engineering and Earth Sciences University of Notre Dame February 27, 2013 CE20140 A. S. Donahue (University of Notre Dame) Lecture 11 1 / 10

2 Outline Homework #5 is due today at 5pm R 2 Review Local vs. Global Variables Sub functions & Nested Functions Anonymous Functions Inline Functions A. S. Donahue (University of Notre Dame) Lecture 11 2 / 10

3 R 2 Review A search for the definition of R 2 can produce many different formulas, each which may produce a different value then the others: Basic Definition Correlation link link MATLAB Sample Code link For our purposes we will use the basic definition for R 2 in this class. However, if you wish to understand more on how Goodness of fit is determined there are many Statistics texts and courses that can shed some light on the technique. A. S. Donahue (University of Notre Dame) Lecture 11 3 / 10

4 Local vs. Global Variables All variables in a function are local. This means that they are created and used locally in the function, but cannot be accessed by other functions or by the Workspace. A variable can be designated as global which makes it available to other functions or the Workspace. The syntax is >> global var1 var2... A variable must be declared as global in all functions that wish to access it. If a variable is declared as global in a script or from the command window it will accessible by the Workspace. Global variables can be used and changed by any function that has access to them. A. S. Donahue (University of Notre Dame) Lecture 11 4 / 10

5 Sub Functions Functions can be imbedded into other functions as sub functions. The functions are typed one after another. This is useful to further organize code without having to carry many more.m files to run your functions. All variables in a sub function are considered local unless otherwise declared. In other words sub functions cannot necessarily access variables from the functions they are embedded in. The basic structure is: function [out1,...] = function_name(in1,...)... [out1,...] = sub_function_name(in1,...)... function [out1,...] = sub_function_name(in1,...) Commands... A. S. Donahue (University of Notre Dame) Lecture 11 5 / 10

6 Nested Functions Functions can also be imbedded into other functions as nested functions. The nested functions are given within the body of the main function. When using nested functions you must finish each nested function and the main function with the end statement. Nested functions are another technique to organizing your code. Variables within the primary function can be accessed and changed by nested functions. Variables within a nested function can be accessed and changed by any function containing that nested function. A. S. Donahue (University of Notre Dame) Lecture 11 6 / 10

7 Nested Functions Multiple Levels It is possible in MATLAB to nest functions within a nested function. Think of when we nest multiple for loops within each other. A nested function can be called from a level above it. A nested function can be called from another nested function at the same level within the primary function. A. S. Donahue (University of Notre Dame) Lecture 11 7 / 10

8 Anonymous Functions Anonymous functions allow you to create quick reference functions for mathematical expressions without having to create a whole new function.m file. Basic Syntax >> function_name (inputs) math_expression For example >> myfun (a,b) a+sqrt(b) myfun >> y = myfun(1,4) y = 3 Anonymous functions can also be fed vectors and matrices. A. S. Donahue (University of Notre Dame) Lecture 11 8 / 10

9 Inline Functions Inline functions are similar to Anonymous functions, but the syntax is different. Syntax >> function_name = inline( math_expression as string ) For example >> myfun = inline( a + sqrt(b) ) myfun = Inline function: myfun(a,b) = a + sqrt(b) >> y = myfun([1 2],[4 9]) y = 3 5 A. S. Donahue (University of Notre Dame) Lecture 11 9 / 10

10 In Class Using an Anonymous or Inline function create a function called temp C that uses the formula C = 5 9 ( F-32) to convert degrees Fahrenheit to degrees Celsius, and then convert todays temperature to Celsius. Download contents of In Class SubNestFunctions and combine all of the functions so that instead of having multiple.m files you only have one primary function with a set of imbedded functions (you may use sub functions or nested functions). A. S. Donahue (University of Notre Dame) Lecture / 10

Chapter 3: Functions and Files

Topics Covered: Chapter 3: Functions and Files Built-In Functions Mathematical Functions User-Defined Functions Function Files Anonymous Functions Function Functions Function Handles Working with Data